The present invention relates to HVAC (heating, ventilation, and air conditioning) systems, particularly those having cooling coils with closely spaced and deep fin arrangements. More particularly, the present invention relates to a novel apparatus and method for cleaning HVAC cooling coils.
HVAC cooling coils are designed to cool air by removing water or water vapor from the air passing across the coils. If the air passing across the coils contains any contamination, the contamination will build up between the thin, closely aligned fins of the coils. (The fins may typically be made of aluminum but they can be copper, stainless steel, or other suitable material.) As this contamination builds up, several harmful things begin to happen. The contamination build-up starts insulating the fins which progressively lowers the thermodynamic heat transfer properties of the entire system. The space between the coils also becomes narrower thereby restricting airflow in the system. This restricted airflow builds pressure in the HVAC system and forces the fan motor to work harder and/or reduces the output of air to the air conditioned spaces fed by the HVAC system. At some point, the buildup of contamination can make the HVAC system not function properly or at all. In a chilled water system, contamination buildup reduces the coil's ability to transfer heat, so the chiller that supplies the hot or cold water has to work harder, thus using more energy. In a DX HVAC system, partially contaminated coils create an increased head pressure on the compressor, making it run at an elevated temperature, which greatly reduces the life of the compressor. The compressor is often the most expensive component in an HVAC system.
Contamination build-up on HVAC system coils can result in the introduction and growth of microbiological organisms (microbials) such as bacteria and fungi (mold). Microbials are ubiquitous in the environment and are brought into the HVAC system through fresh air or make-up air intakes of the system. The microbials in the air are captured in the coils and are introduced into a moist environment with nutrients from built-up contaminants. Since the coils stay moist for long periods of time, the mold and bacteria are allowed to grow. This buildup of microbial growth in coils is commonly referred to as biofilm. When the temperature coming into the system is hot or warm, biofilm growth can take place rapidly. As coils dry out the mold and bacteria can be released into the air in the occupied building through the HVAC duct systems downstream of the coils. Microbials can cause serious health issues to building occupants. Health care facilities are at risk from these airborne microbials due to immunocompromised patients being treated in their buildings.
HVAC coils are supposed to be cleaned routinely to prevent and/or remove contamination build-up that causes the problems outlined above. If cleaning completely removes all contamination without damaging the fins of the coils and the HVAC ductwork also remains clean and dry, the HVAC system would continue to perform as designed without introducing microbials into the building.
The typical procedure for cleaning HVAC coils is to use a pump-up sprayer to apply coil cleaner solution to the upstream and downstream faces of the coil. The cleaner is allowed to stay on the coil for the amount of time recommended by the coil cleaner manufacturer. A garden hose or low pressure sprayer is then used to rinse the coils to remove contaminants from the cooling coil, as well as the coil cleaning chemicals.
Thus, conventional coil cleaning procedures use a garden hose supplying approximately 5-9 gallons per minute flow rate to flush the coil. For thick coils (normally 4″ or greater), or closely spaced coil fins (more than 10 fins per inch), such flow rates can only physically reach a few inches into the cooling coil. Generally, when a thick coil (e.g., eight inches thick or more) is cut so that its cross-section can be inspected, the center of the coil is still impacted with contaminants that the conventional coil cleaning process cannot reach.
The present invention recognizes the foregoing considerations, and others, of the prior art.